FIELD OF THE INVENTION
The invention relates to a breakstem fastener installation tool, more specifically, a tool for installing fasteners each having a stem, part of which stem breaks off on installation of the fastener. The fastener is installed by pulling on the fastener stem with respect to the fastener body, thereby deforming the body of the fastener. Increased pulling on the fastener stem causes the stem to break, leaving part of the stem plugging the body. Commonly the tool is pneumatically powered, with a pneumatically actuated piston and cylinder device for applying force to pulling means (e.g. stem-gripping jaws) for pulling the stem.
The fastener stem must be designed to break at a tension greater than that which is required to fully deform the fastener body; usually this is achieved by forming the stem with a weakened section or breakneck which will fracture at a predetermined tension. Typical values of fracture tension for small breakstem rivets are within the range of 500 lbs force to 1200 lbs force (2224 to 5338 Newtons).
When a fastener is being installed by a tool, the breaking of the fastener stem suddenly releases the resistance to the tension force generated within the tool by the pneumatic piston and cylinder device. This generates a substantial mechanical shock, and air-generated noise, in the tool, which is usually hand held.
The present invention seeks to reduce these effects.